# argparse: command line parser for Erlang

A mini-framework to create complex cli. Inspired by Python argparse.

Follows conventions of  Unix Utility Argument Syntax.

    argparse [-abcDxyz][-p arg][operand]

## Argument parser
Converts list of strings (command line) into an argument map,and a
command path; see [argparse reference](doc/ for detailed description.

## cli mini-framework
Make a step beyond parser, and export existing Erlang functions: [cli reference](doc/

## Basic [example](doc/examples/escript/simple)

cli is naturally suitable for building small escript-based apps:

    #!/usr/bin/env escript

    -export([main/1, cli/0, rm/1]).
    -mode(compile). %% evaluated module cannot contain callbacks

    main(Args) ->
        cli:run(Args, #{progname => "simple"}).

    cli() ->
        handler => {?MODULE, rm},
        arguments => [
          #{name => force, short => $f, type => boolean, default => false},
          #{name => recursive, short => $r, type => boolean, default => false},
          #{name => dir}

    rm(#{force := Force, recursive := Recursive, dir := Dir}) ->
        io:format("Removing ~s (force ~s, recursive: ~s)~n",
            [Dir, Force, Recursive]).

The example above does not have sub-commands, and implements `rm/1`
handler, that serves as an entry point with parsed arguments. Help options are
added automatically:

    $ ./erm --help
    usage: erm [-fr] <dir>

    Optional arguments:
      -r  recursive, [false]
      -f  force, [false]

## Calc: cli with [multiple commands](doc/examples/escript/calc)

Calculator implements several commands, with sub-commands available. Full
source code here: [doc/examples/escript/calc](doc/examples/escript/calc)

Command definitions:

    cli() ->
            commands => #{
                "sum" => #{
                    arguments => [
                        #{name => num, nargs => nonempty_list, type => int, help => "Numbers to sum"}
                "math" => #{
                    commands => #{
                        "sin" => #{handler => {math, sin, undefined}},
                        "cos" => #{},
                        "tan" => #{handler => {math, tan, undefined}}
                    arguments => [
                        #{name => in, type => float, help => "Input value"}
                "mul" => #{
                    arguments => [
                        #{name => left, type => int},
                        #{name => right, type => int}

The calculator provides "sum" command that prints a sum of integer numbers:

    $ ./calc sum 1 2 3

Math sub-commands provide trigonometric functions:

    $ ./calc math cos 1.4
    $ ./calc math sin 1.4

## Complex applications

cli is capable of handling releases containing hundreds of modules
implementing cli behaviour. Commands may be exported from multiple modules and
applications. cli makes best efforts to merge commands exported,
format usage output and error messages.

See example: [doc/examples/multi](doc/examples/multi)

This example contains two modules, multi_math.erl and multi_string.erl.

Use ```rebar3 escriptize``` to build the application. Try various commands,
e.g. ```./multi math cos 1.0```, or ```./multi string lexemes 1+2+3+4 -s +```
to get a feeling!

## Argument [parser alone](doc/examples/escript/erm)

It is possible to use argument parser alone, without the cli mini-framework:

    #!/usr/bin/env escript

    main(Args) ->
        #{force := Force, recursive := Recursive, dir := Dir} =
            argparse:parse(Args, cli()),
        io:format("Removing ~s (force: ~s, recursive: ~s)~n",
            [Dir, Force, Recursive]).

    cli() ->
        #{arguments => [
            #{name => force, short => $f, type => boolean, default => false},
            #{name => recursive, short => $r, type => boolean, default => false},
            #{name => dir}

## Help and usage information
cli automatically prints usage, if command line parser reports an
error. An attempt is made to guess the most relevant command.
Argument help can be customised.

## Build
This project requires OTP-22 or above. Simple integration is available via Hex and

    {deps, [argparse]}.

## Known incompatibilities
In comparison with Python implementation, `argparse` for Erlang:
  * boolean flag (option) automatically uses {store, true}
  * all positional arguments are required by default (even when nargs is 'maybe')
  * first-class (sub) commands, slightly differently from argparse
  * implicit --help/-h is not a part of argparse (but implemented in cli)

Commands vs. positional arguments: command always takes precedence
over a positional argument.
Commands form exclusive groups, e.g. only one command can
be followed at a time.

## Supported command line syntax
 * command (priority positional argument) : ectl {crawler|reader|writer}
 * command, and sub-command:                ectl crawler {start|stop|check}
 * positional argument (required):          ectl <arg1> <arg2>
 * positional argument (with default):      ectl [<arg1>]
 * boolean flag:              ectl [-rf]
 * required flag:             ectl -r
 * short optional argument:   ectl [-i <int>]
 * short optional:            ectl [-i [<int>]]
 * required short option:     ectl -i <int>
 * long option flag:          ectl [--foo]
 * long optional argument:    ectl [--foo <arg>]
 * required long:             ectl --foo <arg>
 * long, arg=value form:      ectl --foo=arg
 * list of arguments:         ectl <arg>, ...

## Expected features

To be considered after 1.2.0:
* search for commands and arguments (mini-man)
* abbreviated long forms
* mutual exclusion groups
* shell auto-complete
* automatically generated negative boolean long forms "--no-XXXX"

## Changelog

Verson 1.2.4:
 * minor spec fixes

Verson 1.2.3:
 * implemented global default
 * minor bugfixes

Verson 1.2.1:
 * minor bugfixes, support for choices of atoms

Version 1.2.0:
 * CLI incompatible change: `cli:run/1,2` by default now calls halt(1) in case of a parser error
 * bugfixes

Version 1.1.3:
 * added `help => hidden` for commands and options
 * changed default formatting for better readability
 * fixed bug causing `nargs => all` to be ignored

Version 1.1.2:
 * support for "--arg=value" form

Version 1.1.1:
 * added templates for help text

Version 1.1.0:
 * Handler support for minimal CLI
 * cli/1 optional behaviour callback deprecated
 * Ability to provide progname as an atom

Version 1.0.2:
 * Improved documentation
 * Validation run for CLI commands

Version 1.0.0:
 * First public release

Version 0.1.0:
 * First usable version (API is unstable yet)